Siemens SIMATIC NET CP 443-1 OPC UA Improper Input Validation (CVE-2016-4956)

medium Tenable OT Security Plugin ID 501094


The remote OT asset is affected by a vulnerability.


ntpd in NTP 4.x before 4.2.8p8 allows remote attackers to cause a denial of service (interleaved-mode transition and time change) via a spoofed broadcast packet. NOTE: this vulnerability exists because of an incomplete fix for CVE-2016-1548.

This plugin only works with Tenable.ot.
Please visit for more information.


The following text was originally created by the Cybersecurity and Infrastructure Security Agency (CISA). The original can be found at

Siemens has identified the following specific workarounds and mitigations users can apply to reduce the risk:

- Deactivate NTP-based time synchronization of the device, if enabled. The feature is disabled by default.
- Configure an additional firewall to prevent communication to Port UDP/123 of an affected device.

As a general security measure, Siemens strongly recommends users protect network access to devices with appropriate mechanisms. In order to operate the devices in a protected IT environment, Siemens recommends users configure the environment according to Siemens operational guidelines for industrial security, and follow the recommendations in the product manual.

Additional information on industrial security by Siemens can be found at:

For more information about this issue, please see Siemens security advisory SSA-211752

See Also

Plugin Details

Severity: Medium

ID: 501094

Version: 1.2

Type: remote

Family: Tenable.ot

Published: 5/2/2023

Updated: 7/24/2023

Supported Sensors: Tenable OT Security

Risk Information


Risk Factor: Low

Score: 1.4


Risk Factor: Medium

Base Score: 5

Temporal Score: 3.7

Vector: CVSS2#AV:N/AC:L/Au:N/C:N/I:N/A:P

CVSS Score Source: CVE-2016-4956


Risk Factor: Medium

Base Score: 5.3

Temporal Score: 4.6

Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Temporal Vector: CVSS:3.0/E:U/RL:O/RC:C

Vulnerability Information

CPE: cpe:/o:siemens:simatic_net_cp_443-1_opc_ua_firmware

Required KB Items: Tenable.ot/Siemens

Exploit Ease: No known exploits are available

Patch Publication Date: 7/5/2016

Vulnerability Publication Date: 7/5/2016

Reference Information

CVE: CVE-2016-4956


GLSA: GLSA-201607-15

SuSE: SUSE-SU-2016:1563, SUSE-SU-2016:1584, SUSE-SU-2016:1602, openSUSE-SU-2016:1583, openSUSE-SU-2016:1636